Project Summary The prospect of using stem cells for therapeutic purposes has been one of the most promising fields of science and medicine in recent years. Progress in this area has been substantial, including a better understanding of stem cell biology, the identification of new sources of stem cells, and encouraging therapeutic results in a variety of diseases. Stroke remains one of the greatest challenges in medicine, with little or no effective treatments available. Preclinical studies using stem cells have been encouraging and have led to the initiation of a few clinical trials. Unfortunately, none of these trials demonstrated a satisfactory therapeutic outcome. There are many suggested reasons for that failure, with one of the primary reasons being an inefficient biodistribution of stem cells and hostile unsupportive microenvironment after stroke. Intraarterial delivery could potentially bypass this limitation, and a few attempts have been made to use this approach for direct targeting of brain lesions. In previous studies, we exploited VLA-4/VCAM-1 pathway and demonstrated that glial restricted progenitors engineered to overexpress VLA-4 can be efficiently targeted to stroke lesion after intraarterial injection. We applied non-invasive longitudinal MRI and multiphoton microscopy and demonstrated that in addition to efficient docking at the surface of cerebral endothelium they also undergo diapedesis into brain parenchyma. This is exciting but we encountered a challenge. After arriving in the hostile environment of stroke parenchyma, GRPs do not proliferate and do not myelinate efficiently. To address this challenge, we propose a strategy to support function of GRPs by co-injection with miRNAs-loaded liposomes. Specific targeting of both GRPs and miRNAs to stroke injury will be accomplished by our established VLA- 4/VCAM-1 platform. To optimize delivery of both therapeutic agents we propose to monitor the procedure of targeting with novel molecular magnetic resonance imaging - chemical exchange saturation transfer (CEST). This imaging method enables selective detection of individual CEST- contrast agent allowing multi-color imaging. This quality makes it possible to independently image injection of the therapeutic cells as well as miRNA-carrying liposomes and optimize the transplantation parameters for the most efficient delivery of both elements. We will perform in vitro screening for miRNAs that support function of GRPs with the main focus being their proliferation and differentiation towards myelinating oligodendrocytes. Once the image-guided co- injection protocol is established and best miRNA candidates are identified, we will proceed to testing therapeutic efficacy in MCAO mouse model.